Methacryloxypropyl-functional organosilicon compounds readily copolymerize with radically polymerizing monomers such as methyl methacrylate and styrene. For this reason they are often used as starting materials for copolymers and as modifiers for polymers prepared from the polymerizing monomers. Among the methacryloxypropyl-functional organosilicon compounds, methacryloxypropyldimethylchlorosilane is typically employed as an endblocker or terminating agent for methacryloxy-functional silicone macromonomers. Methacryloxypropyldimethylchlorosilane is generally prepared by an addition reaction between allyl methacrylate and dimethylchlorosilane followed by isolation by distillative purification of the reaction product (see Polymer, Volume 26, page 437, 1985). One drawback that has generally been associated with this method is the pronounced tendency for gelation to occur during the reaction and distillative purification. Another drawback to this method has appeared when its methacryloxypropyldimethylchlorosilane product is used as an endblocker for methacryloxy-functional silicone macromonomers. Specifically this drawback is the frequent occurrence of low copolymerization conversions with radically polymerizing vinylic organic compounds.
It has now been found that alpha-methylpropionyloxypropyldimethylchlorosilane is produced as an impurity in the methacryloxypropyldimethylchlorosilane and that this impurity causes the reduced copolymerization conversions with radically polymerizing vinylic organic compounds. It has been also found that the production of the alpha-methylpropionyloxypropyldimethylchlorosilane impurity can be substantially reduced by reducing the water content in the starting allyl methacrylate to the maximum extent possible.
Therefore, it is an object of the instant invention a method for the preparation of methacryloxypropyldimethylchlorosilane that is very efficient, yields a very pure methacryloxypropyldimethylchlorosilane, and produces little alpha-methylpropionyloxypropyldimethylchlorosilane impurity.